btvvc32.drv expect the "Depth" byte in avi to be 0x0c (12) but ffmpeg avi muxer sets this byte to 0x18 (24) so y41p muxed in avi with ffmpeg are causing mplayer to crash when using bt411 codec (btvvc32.drv).

Once you change that byte to 0x0c in hex editor files plays fine with mplayer -vfc bt411